1. Field of the Invention
The present invention provides a method and apparatus for determining whether the interior of a container neck has the desired shape and, more specifically, for determining whether container necks have a desired cylindrical configuration or have undesired ovality or other deformity.
2. Description of the Prior Art
It has been known to manufacture plastic bottles out of a wide variety of materials such as polyethylene terephthalate (PET), for example, for use as beverage containers. In such manufacture it has been known to create preforms by injection molding and to subsequently convert these preforms into containers as by a blow-molding bottle-forming process.
One of the problems encountered in connection with this type of bottle manufacture is that frequently the bottle necks of the preforms which are to be of generally cylindrical shape and have external threads for securing a closure thereto are not of the desired round or cylindrical configuration, but rather contain a defect in shape. A common defect of this type is ovality wherein the preform container neck has an oval rather than round shape.
One of the reasons such a preform may have ovality is that the preform may warp during cooling after molding. A second reason for ovality is that a preform which is still warm may be partially crushed as it is unloaded from the injection molding machine.
Another common defect is an indentation caused by localized forces from a relatively sharp object. Although the localized forces may be applied at a point in the finish region other than near the open end, the open end will be deformed.
Attempts to convert an oval or otherwise out of shape preform into a bottle create problems In the blow-molding bottle-forming process, the preforms are placed on spindles designed to fit inside the threaded neck of the preform. An oval preform will not fit properly on the spindle and this leads to production problems. In the event that the oval or otherwise out of shape preforms survive the production process, they will be made into bottles the threaded neck of which may not fit a threaded cap, thus causing undesired loss of carbon dioxide or even product from the container.
There is a substantial need for an inspection system which will determine whether the container neck has the desired shape or has ovality or other undesired defects.